Cloaking device A device invisible to a static magnetic field that could have practical military and medical applications has been developed by European researchers.

Fedor Gomory and colleagues in Slovakia and Spain designed a cloak for a direct current, or DC, magnetic field that is static and produced by a permanent magnet or coil carrying a direct current.

DC magnetic fields are used in MRI imaging devices, in hospitals and in security systems, such as those in airports.

The researchers' device, described in the journal Science, features a cylinder with two concentric layers. While the inner layer consists of a superconducting material that repels magnetic fields, the outer layer is a ferromagnetic material that attracts them.

Placed in a magnetic field, the device has no effect on the field lines, showing neither a shadow nor a reflection. So an object inside the device cannot be detected.

"There are many applications - for some cars, ships or a submarine," says study co-author Alvaro Sanchez of the Autonomous University of Barcelona.

He says the device could also be used for patients who have a pacemaker and need a MRI of a knee or other body part, so the image would not be distorted.

Because it is made from commercially available materials, as well as operating under relatively strong magnetic fields and relatively warm liquid nitrogen temperatures, the device could easily be put to practical use, according to the authors.

"For the submarine, you have to make a shell around the submarine that will make the submarine magnetically undetectable," says Sanchez.

"This could also be used to protect some (military and medical) equipment against electromagnetic disturbances."